Within electrical networks contactors are often used for switching large electric currents. These contactors are designed for switching load currents that occur during normal conditions in various applications. The contactor is designed so as to be able to make, conduct and break the electric current.
Electromagnetically operated contactors typically comprise a spring-biased armature moving between two end positions. The armature is a part of an electromagnetic circuit. At a first end position the armature is open and the current path is then open, and at a second end position, the armature is closed and the contactor is then closed, thereby providing an electrical path. Normally contactors are monostable devices and the position of rest is the open position but the opposite positions are sometimes used. The armature is arranged to move a moving contact element relative fixed contact elements, thus breaking the electrical path when moving the moving contact element away from the fixed contact elements and making contact by the reverse movement. The movement of the armature is accomplished by energizing a coil of the electromagnetic circuit, the coil typically being wound around parts of either the armature or around a fixed part of the electromagnetic circuit.
Operation of such contactor entails applying a voltage over the coil, giving a current through it, whereby a magnetic flux is produced in the electromagnet. The magnetic flux attracts the armature, which forces contacts of the contactor to close. In the closed state, separation springs and contact springs of the contactor device are all biased and contain high potential energy. When an opening of the contactor is required, the electromagnetic circuit is de-energized whereby the opening is initiated. When the electromagnet is released, the potential energy in the springs is converted to kinetic energy and the armature holding a moving contact element moves rapidly towards its open position. In order to avoid bouncing effects and/or high mechanical impact in the contactor caused by this movement, this kinetic energy needs to be taken care of.
The use of rubber dampers is a known way of reducing the kinetic energy by absorbing the energy. However, although the rubber dampers may absorb up to 50% of the energy, these are not sufficient since the remaining energy causes so-called back travel, wherein the contactor elements of the contactor are moving towards a closed state again. This increases the risk of re-closing the contactor.
Another feasible solution would be to use hydraulic dampers or other advanced dampers, but such solutions are costly and are typically only viable in particular high-end applications.
Still another solution is to use the electromagnet of the contactor as a brake during the opening process. EP 2 551 881 is one example of using the electromagnet for reducing the velocity of the moving armature. The polarity of a power supply for the coil of the contactor is reversed whereby a deceleration is accomplished.